In the current tire vulcanization process, in order that the air in the mold cavity is released and the rubber could be uniformly distributed in the mold, the existing tire molds each has a plurality of exhaust holes on the mold cavity. The required exhaust holes are usually formed through drilling. However, the burrs of the holes need to be trimmed after the drilling process, which increases the mold manufacturing process and the mold manufacturing cost. On the other hand, in the vulcanization process, the exhaust gas in the tread region is discharged through circular exhaust holes usually located at the top of the inner tube of the mold and penetrating to the outer surface of the mold. Under the conditions of high temperature and high pressure, the unvulcanized raw rubber is extruded outside the top cavity of the mold. When the air is discharged from the mold, the rubber is extruded into the drilled exhaust holes to form rubber furs, some of which may be broken in the exhaust holes of the mold and hinder the air discharge from the cavity, thus the rubber cannot fully fill the entire mold cavity. In order to avoid this, the tire molds shall be removed from the production line for a cleaning. The common cleaning operation is to compel the rubber out of each pore with a drill bit, which consumes a lot of time and affects the production efficiency. Most of the rubber furs stand on the tire after demolding, and in order to remove the rubber furs, special persons and corresponding devices have to be required to trim the rubber furs, which not only affects the appearance quality of the tire, but also wastes the rubber material and increases the production cost.
In order to overcome the above defects, a pore-free technique for the tire segmented mold is proposed, such as the U.S. patent No. US20070009623, which mounts a mass of relatively thin annular plates side by side in the housing of two opposite half molds or a segmented mold, and forms gaps on one side or two sides of the ply. When the tire is vulcanized, gas is discharged via the gaps to ensure that the vulcanized tire has a smooth surface. However, the mold structure of US20070009623 has no a circumferential exhaust slot and its exhaust gas is discharged to the back of the pattern block through the radial exhaust slot. Thus the distance is long, the exhaust effect is poor, and a blocking easily occurs. Once a blocking occurs, it is difficult for cleaning as the distance is too long. In addition, the back of the pattern block fits the sliding block, and a lot of exhaust slots shall be machined on the fitting surface to guide air, which increases the machining cost.
In addition, there are many types of tire patterns, and being restricted by the professional requirements such as pitch and steel sheet embedding, most of the molds of pore-free structures divided transversely cannot be disassembled. In addition, the mold structure of US20070009623 is open around and cannot be blocked. Thus, if the mold structure cannot be disassembled, it cannot be cleaned once being blocked.
In conclusion, although the tire vulcanized with the existing pore-free technique has a good appearance and saves the rubber material, there are still significant technical difficulties that hinder the promotion and popularization of the pore-free technique, i.e., the exhaust effect of the pore-free mold is poor and the cleaning is difficult. Almost all of the pore-free molds have a complex cleaning process and a high cost, and mostly cannot be cleaned completely, thereby directly affecting the quality and cycle of the re-vulcanization of the mold.